The present invention relates to an exposure apparatus for transferring a pattern of a master such as a mask onto a photosensitive substrate such as a semiconductor wafer through a projection optical system, an imaging performance measurement method, a device manufacturing method, a semiconductor manufacturing factory, and an exposure apparatus maintenance method and, more particularly, to an imaging performance measurement method for a projection optical system and particularly, a coma measurement method.
In manufacturing semiconductor devices in the photolithography process, a projection exposure apparatus has been used to transfer a circuit pattern or the like formed on a reticle, photomask, or the like (to be referred to as a reticle hereinafter) onto a semiconductor wafer or the like coated with a photoresist. An exposure apparatus of this type is required to accurately transfer the pattern on the reticle onto the wafer at a predetermined magnification (reduction ratio). To meet this requirement, it is important to use a projection optical system excellent in imaging performance and almost free from aberrations. Patterns, resolutions of which exceed the general imaging performance of an optical system, have often been transferred due to recent demand for finer micropatterning of semiconductor devices. As a result, patterns to be transferred are more sensitive to aberrations of an optical system. An increase in exposure area and a high NA (Numerical Aperture) are required for a projection optical system. This makes it more difficult to correct aberrations.
Under these circumstances, a strong demand has arisen for measuring imaging performance and particularly coma of a projection optical system while the projection optical system is mounted in an exposure apparatus, i.e., while the exposure apparatus is actually used for exposure.
As a conventional method of measuring imaging performance, e.g., aberration of a projection optical system, a method is available to measure wave aberration of a projection optical system using an interferometer in the manufacture/adjustment with a projection lens alone. Another method is also available to observe the aerial image of a reticle or mask pattern which is formed through the projection optical system and calculating the imaging performance of the projection optical system from the aerial image. Still another method is available to project and expose about five line-end-space marks on a resist applied to a wafer, measure with a scanning electron microscope (SEM) the line width and shape of a resist image left upon development, and measure the imaging performance and particularly coma from the line width difference between or asymmetry of shapes of two lines at two ends. Recently, still another method is also known (Japanese Patent Laid-Open No. 11-237310) in which a small line width pattern is projected and exposed on a resist, a large line width pattern is then multiple-exposed on the small pattern, and relative misalignment between the patterns is measured by an alignment test device using the resist image left upon development.
Either method is unsatisfactory in calculating imaging performance of the projection optical system on the semiconductor exposure apparatus. First, in the method using the interferometer, the arrangement of a wave aberration measurement device is bulky to require a very large space. In addition, the optical arrangement of the wave aberration measurement device is greatly different from that of the semiconductor exposure apparatus. It is currently expected to be difficult to mount the interferometer in the exposure apparatus.
In the method of observing an aerial image, an aerial image observation optical system must be mounted in a wafer stage. The wafer stage of an exposure apparatus is generally movable at a very high speed from the viewpoints of throughput and control accuracy. It is very disadvantageous to mount the observation optical system in the wafer stage due to the weight. In addition, the internal space of the wafer stage is limited, and the observation optical system mounted inside the wafer stage must also be downsized. On the other hand, the aberration of the observation optical system must be minimized due to the function of measuring the aberration as the imaging performance of the projection optical system. This makes it difficult to downsize the observation optical system, resulting in a contradiction.
The method of observing the exposed resist image with the SEM allows obtaining imaging performance (aberration) in a state wherein the projection optical system is mounted on the main body. However, development and SEM measurement are required to evaluate the resist image, resulting in time-consuming and cumbersome operation.
It is an object of the present invention to solve the conventional problems described above, calculate imaging performance such as coma of a projection optical system with a simple arrangement without any development or SEM measurement, and hence perform exposure in a state of excellent imaging performance.
In order to achieve the above object, an exposure apparatus according to the present invention is an exposure apparatus for projecting and exposing a transfer pattern formed on a master such as a reticle onto a substrate such as a semiconductor wafer placed on a movable stage (wafer stage), characterized by comprising a step mark formed from a step and placed on the movable stage and preferably a stage reference mark, an image reception section for imaging the step mark on an image sensing element at an exposure wavelength through a projection optical system, and a data processing section for calculating imaging performance of the projection optical system on the basis of image data obtained from the image reception section.
An imaging performance measurement method according to the present invention is a method of measuring imaging performance of a projection optical system, characterized by comprising the steps of placing a step mark formed from a step near an image plane of the projection optical system, making an image sensing element sense an image of the step mark through the projection optical system using light having a wavelength used for the projection optical system, and calculating the imaging performance of the projection optical system on the basis of sensed image data.
A device manufacturing method according to the present invention is characterized by comprising the steps of installing manufacturing apparatuses for performing various processes including an exposure apparatus in a semiconductor manufacturing factory and manufacturing a semiconductor device through a plurality of processes using the manufacturing apparatuses. In addition, the device manufacturing method may comprise the steps of connecting manufacturing apparatuses via a local area network and communicating data information about at least one of the manufacturing apparatuses between the local area network and an external network outside the semiconductor manufacturing factory. A database provided by an exposure apparatus vendor or user may be accessed via the external network to perform data communication, thereby obtaining maintenance information of the manufacturing apparatuses. Alternatively, data communication may be performed with another semiconductor manufacturing factory different from the semiconductor manufacturing factory via the external network to perform production management.
A semiconductor manufacturing factory according to the present invention is characterized by comprising manufacturing apparatuses for performing various processes including the above exposure apparatus, a local area network for connecting the manufacturing apparatuses, and a gateway for allowing access from the local area network to an external network outside the factory, wherein data information about at least one of the manufacturing apparatuses can be communicated.
An exposure apparatus maintenance method according to the present invention is characterized by comprising the steps of making an exposure apparatus vendor or user provide a maintenance database connected to an external network outside a semiconductor manufacturing factory, allowing access from the semiconductor manufacturing factory to the maintenance database via the external network, and transmitting maintenance information stored in the maintenance database to the semiconductor manufacturing factory via the external network.
According to the present invention, the image of the step mark is imaged using the light having the wavelength used for the projection optical system through the projection optical system. The imaging performance and particularly coma of the projection optical system can be evaluated on the basis of the image data of the step mark. As a result, the imaging performance and particularly coma of the projection optical system can be calculated on the semiconductor exposure apparatus with a very simple arrangement without any development or SEM measurement.
Exposure can always be performed in a good aberration state by adjusting the aberration of the projection optical system on the basis of the calculated aberration.
Aberration measurement can be done upon a change in an exposure condition, or aberration measurement can be performed during continuous exposure. Aberration can be adjusted as needed to always allow exposure in a good aberration state.
Other objects and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention which follows. In the description, reference is made to the accompanying drawings, which form a part thereof, and which illustrate an example of the invention. Such an example, however, is not exhaustive of the various embodiments of the invention, and, therefore, reference is made to the claims which follow the description for determining the scope of the invention.